@ninahaskin Most seeds will germinate faster with heat. Vegetables can germinate in 50 ºF soil, but ideally prefer 80 or so! I do my seeds in the basement ona shelf, and that's between 50 and 60 right now. Cool, but doable. Take Tomato, for instance. At 50ºF that's close to 40 days. At 60, it's more like 15, and at 80 it's 6 days, on average.

The Cukes, squash, and pumpkin I did above, would take 30 -40 days at 50ºF, so, I can cut that to a week or so, by using the heat mat. It raises the temps about 20ºF compared to ambient.

I use the heat mats under my seed starter trays, too, for the same reason: Faster germination. These Ziplocs will be opened in about 6 days, (I'll hold them up to the light each day at 4 days on... to check for germination) and then, I'll take the seedlings, and plant them into 3 or 4 inch (7cm to 10cm) pots, and eventually, after hardening off, into the 10 Gallon (37 liter) Grow Bags outside.